Process of making molds



Patented Jan. 9, 1934 UNITED STATES PATENT OFFICE No Drawing. Application May 21, 1932 Serial No. 612,865

Claims.

Heretofore in making molds for molding metal castings for foundry work it has been the general practice to bake said mold in order to harden and set same prior to use, and suitable binders have been mixed with the sand, which became hard and dry upon baking.

This baking process entailed an unnecessary expense and delay, and in making certain types of castings the molds were not strong enough, even after baking, to withstand the rough handling to which they are subjected, and became broken, chipped and unfit for use.

The present process or method has in view the provision of a mold which does not require baking, is self-venting, and which at the same time is harder and more rugged than the baked molds of the prior art and is much more readily made.

The present method consists in making a binding agent by mixing a combustible or inflammable compound such as a solution of celluloid with a volatile solvent such as acetone, butanol, etc., forming a paste. The consistency of the paste is preferably such that it has a very slight tendency to flow and at the same time can be readily handled with a paddle or the like. This binder paste is then mixed with a suitable grade of sand in the proportion of from ten to twentyfive per cent. of paste to the amount of sand re- 30 quired, and this mixture of sand and paste is then used as a facing for the mold, having a sufficient depth to form a rigid structure. The balance of the mold is then made up of green sand.

As an alternative to the above, the celluloid solvent mixture may be made in such proportions as to be sufficiently fluid to permit spraying, and a mold may be made up of sand in the usual manner from green sand or other suitable prodnot and the face or surface of the mold may be 40 sprayed with the celluloid and solvent mixture so as to impregnate the sand with the binder and form a rigid self-sustaining structure.

The solvent will evaporate in either of the above methods to such an extent by air drying only without the use of heat or baking that the molds will be of a rigid structure and can be readily handled after they have stood for about onehalf hour and such molds may be used within approximately two hours after being made. The celluloidcontent of the binder completely bums away during the casting operation so that the mold sand may be readily removed from the completed casting article.

Experience has shown that the celluloid solvent mixture divides the binding of the mold sand only the facing of the mold from said impregwhich strains the mold sufiiciently to eliminate the necessity of using a metallic stiffener and holds the face of the mold intact when it first comes in contact with the hot metal, while at the same time the bond formed by the celluloid is of such a nature as to allow the free venting of the mold and consequently absence of tendency to blow.

I claim: 1. The process of making molds for metal castings which consists in mixing a solution of celluloid with a volatile solvent such as acetone or butanol, impregnating the mold sand with said celluloid and solvent mixture and forming nated sand.

2. In the process of making sand articles such as molds for metal castings, the steps of which consist in mixing a solution of celluloid with a volatile solvent to form a binder and forming only the facing of the mold from a mixture of said celluloid solvent and sand.

3. The process of making sand articles which consists in mixing a solution of celluloid with a volatile solvent to form a binder and impregnating that portion of the sand from which only the facing of said article is formed with said celluloid and solvent mixture, permitting said solvent to evaporate by air drying whereby said celluloid will remain in the sand to bind the particles thereof into a rigid structure.

4. As an article of manufacture, a mold for casting metal having only the facing of its body formed from a mixture of sand and a solution of celluloid and a volatile solvent, the sand predominating over the celluloid and solvent and the article being air dried to evaporate the major portion of the solvent.

, 5. As an article of manufacture, a mold for casting metal having only its face portion composed of a mixture of sand and a solution of celluloid and a volatile solvent. the sand predominating materially over the celluloid and solvent and the article being air dried to evaporate the major portion of the solvent.

WILLIAM H. WALTER. 

